The present invention relates to a polycarbonate resin composition, and more particularly it relates to a polycarbonate resin composition having an excellent resistance to an ionizing radiation, which exhibits a low discoloration without deterioration in properties thereof when exposed to the ionizing radiation for sterilization.
Polycarbonate resins have been widely utilized in the fields of medical supplies and appliances because the polycarbonate resin have excellent mechanical strength, impact resistance, heat resistance and transparency as well as a high safety. The medical supplies and appliances are generally sterilized upon use. Specifically, the sterilization of these medical supplies and appliances has been carried out by a high-pressure steam sterilization process, an ethyleneoxide gas (EOG) sterilization process, or a sterilization process using an ionizing radiation such as a gamma radiation or an electron beam. Among these sterilization processes, the high-pressure steam sterilization process has disadvantages such as high energy cost and necessity of a drying step after the sterilization. Similarly, the EOG sterilization process has posed such problems as toxicity of ethyleneoxide itself or environmental pollution upon disposal thereof. Under these circumstances, a recent tendency is such that the sterilization process using an ionizing radiation, generally a gamma radiation has been predominately adopted because the sterilization process is relatively inexpensive and can be performed at a low temperature in a dry condition.
However, there also is such a problem that the polycarbonate resin suffers from yellow discoloration when exposed to the ionizing radiation for sterilization thereof. This results in considerable deterioration in value of the products, especially when the polycarbonate resin is applied to the medical supplies or appliances.
As means for solving these problems, there have been proposed a method in which a halogen-containing polycarbonate resin is used (Japanese Patent Application Laid-open (Kokai) No. 2-55062 (1990)), a method in which a brominated phthalic acid derivative is blended (Japanese Patent Application Laid-open (Kokai) No. 5-179127 (1993)), or the like. However, in these methods, metal corrosion is likely to generate due to the inclusion of halogen in the resin compositions, so that a molding machine or the like therefor are required to be formed from special metal material having a corrosion resistance.
In order to solve the afore-mentioned problems such as yellow discoloration or the like, there have been also proposed a method in which thio-alcohols are used (Japanese Patent Application Laid-open (Kokai) No. 1-229052 (1989)), a method in which thio-ethers are used (Japanese Patent Application Laid-open (Kokai) No. 2-115260 (1990)), a method in which compounds having a mercapto group are used (Japanese Patent Application Laid-open (Kokai) Nos. 2-49058 (1990), 4-36343 (1992) and 6-166807 (1994)), a method in which polyalkylene-oxide and an aromatic compound having a sulfonate group are used in combination (Japanese Patent Application Laid-open (Kokai) No. 5-209120 (1993)), and a method in which compounds having a sulfide group are used (Japanese Patent Application Laid-open (Kokai) No. 6-93192 (1994) and 6-248170 (1994)). However, in these methods, there still exist such problems that the yellow discoloration cannot be sufficiently prevented, or deteriorated environmental conditions occurs due to generation of malodor upon forming, or the like.
Furthermore, in order to solve the afore-mentioned problems, Japanese Patent Application Laid-open publication (Kokai) No. 61-215651 (1998) discloses a method in which boron compounds are used, Japanese Patent Application Laid-open (Kokai) No. 62-135556 (1987) discloses a method in which polyether-polyol or an alkyl ether thereof are used, Japanese Patent Application Laid-open (Kokai) Nos. 64-22959 (1989) and 1-161050 (1989) disclose a method in which polyether-polyol protected by particular terminal groups are used, Japanese Patent Application Laid-open publication (Kokai) Nos. 1-270869 (1989) and 2-13460 (1990)) disclose a method in which polypropylene glycol is used, Japanese Patent Application Laid-open (Kokai) No. 2-232258 (1990) discloses a method in which benzyl alcohol derivatives are used, and Japanese Patent Application Laid-open (Kokai) No. 2-132147 (1990) discloses a method in which itaconic acid, benzaldehyde-dimethylacetal, benzaldehyde-propyleneglycolacetal, etc. are used. However, these methods have also posed such problems that the yellow discoloration cannot be sufficiently prevented or otherwise, if the amounts of the compounds used therein increases to an extent enough in order to prevent the yellow discoloration, the other properties of the polycarbonate resin compositions are adversely affected.
In view of these problems encountered in the prior arts, a polycarbonate resin composition which is capable of exhibiting little deterioration of the inherent properties thereof, little generation of malodor upon forming and little generation of the yellow discoloration upon irradiation of an ionizing radiation for sterilization are strongly demanded.
As a result of the present inventors' intense studies for solving the afore-mentioned problems, it has been found that by blending an oxy group- or a carbonyl group-containing aromatic compound and a specific compound are blended with a polycarbonate resin at specified blending ratios, the obtained polycarbonate resin composition not only maintains inherent properties of polycarbonate resin without deterioration but also prevents generation of yellow discoloration upon sterilization using an ionizing radiation. The present invention has been achieved on the basis of the findings.